Quick question on newlines..

Quick question on newlines..

Neil Black

Member #7,867

October 2006

Yeah, I know it isn't that hard to do. But when I was first starting out I had no idea how to do it.

OICW

Member #4,069

November 2003

Reminds me of myself five years ago (that's approximately how that thread is old).

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Edgar Reynaldo

Major Reynaldo

May 2007

I have a question about the modified version of Kitty Cat's multi line text output. Specifically the line :

           *(next++) = '\n';

From :

1void my_textout1(const char *str, int x, int y)
2{
  char *str_copy = strdup(str);
  char *cur, *next;
5 
  cur = str_copy;
  while(cur)
  {
      next = strchr(cur, '\n');
      if (next)
      {
          *next = 0;
          *(next++) = '\n';
      }
      cur = next;
  }
17 
  free(str_copy);
19}

Since a copy is being worked on , the newline doesn't need to be replaced , just setting the address to the next character should suffice. What I don't understand is why the character after the detected newline should be set to a newline? Isn't "*(next++)" the same as "*(next + 1)"? Since 'cur' gets set to the character position right after where the newline is detected and that character position's value has been set to a newline , why doesn't strchr(cur , '\n') keep returning the same value as 'cur'?

In any case , I came up with another version , based on Kitty Cat's as well :

1 
2void multiline_textout_v1(BITMAP* bmp , FONT *font , const char *ml_str , int x , int y , int v_spacing , int fg , int bg) {
// note that this will only output the text lines of ml_str if each one ends with a newline '\n' character
//   so "Line 1\nLine 2\n" would work , but not "Line 1\nLine 2"
//   And so a normal string would not work either - ("Line 1") would fail 
//     due to the lack of a newline character
char* copy = strdup(ml_str);

char* line = copy;
char* endline = strchr(line , '\n');

while(endline) {
  *endline = '\0';
  textout_ex(bmp , font , line , x , y , fg , bg);
  endline = strchr(line , '\n');
  line = endline + 1;
  y += v_spacing;
}

free(copy);
21}

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Mark Oates

Member #1,146

March 2001

Openlayer's TextRenderer does newlines automatically. 8-)

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Kitty Cat

Member #2,815

October 2002

Quote:

Since a copy is being worked on , the newline doesn't need to be replaced , just setting the address to the next character should suffice.

Correct. A mistake on my part..

Quote:

What I don't understand is why the character after the detected newline should be set to a newline? Isn't "*(next++)" the same as "*(next + 1)"?

No. next++ post-increments the 'next' variable. It increments the variable, but "returns" the original value. ++next would increment the variable and give the new value.

A fixed version of my code would be:

1void my_textout(BITMAP *bmp, FONT *f, const char *str, int x, int y, int fg, int bg)
2{
  char *str_copy = strdup(str);
  char *cur, *next;
5 
  cur = str_copy;
  while(cur)
  {
      next = strchr(cur, '\n');
      if(next) *(next++) = 0;
      textout_ex(bmp, f, cur, x, y, fg, bg);
      y += text_height(f);
      cur = next;
  }
15 
  free(str_copy);
17}

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Edgar Reynaldo

Major Reynaldo

May 2007

Quote:

No. next++ post-increments the 'next' variable. It increments the variable, but "returns" the original value. ++next would increment the variable and give the new value.

Weird. Not what I would expect to happen given that it's in parentheses. I never thought of post-incrementation as returning the original value.

Had to fix a bug in the version I put up and I also added in a function pointer parameter for which text function gets called. So now you can call textout_ex , textout_centre_ex , or textout_right_ex as an input parameter. My version now also displays the trailing end of the string containing newlines so you don't have to end it with a newline character. Use the v_spacing parameter to control the vertical spacing , and enter one of the three aforementioned allegro text functions for the text_func parameter.

Revised code :

1 
2void multiline_textout_v1a(BITMAP* bmp , FONT *font , const char *ml_str , int x , int y , int v_spacing , int fg , int bg ,
                            void (*text_func) (BITMAP* , const FONT* , const char* , int , int , int , int)) {
4 
char* copy = strdup(ml_str);

char* line = copy;
char* endline = strchr(line , '\n');

while(endline) {
  *endline = '\0';
  text_func(bmp , font , line , x , y , fg , bg);
  line = endline + 1;
  endline = strchr(line , '\n');
  y += v_spacing;
}
endline = strchr(line , '\0');
if (line != endline) {
  text_func(bmp , font , line , x , y , fg , bg);
}

free(copy);
23}